The subject matter disclosed herein relates to a heat exchanger and in particular to a bleed flow precooler for use with an aircraft environmental control system.
Aircraft have power systems that are comprised of several components, such as the engine, the environmental control system and a thermal management system. These systems are designed relatively independently from each other with power being transferred from one system to another.
The environmental control system supplies pressurized air to the cabin and flight deck. This is typically accomplished by using an air cycle machine. Air, referred to as bleed air, is removed from the compressor stage of the engine. The bleed air leaves the engine at a high temperature (e.g. greater than 1000° F.) and needs to be cooled prior to further use. The bleed air extracted from the engine is typically cooled by an engine or pylon mounted precooler (HX) that uses engine fan air as the heat sink. The precooler keeps the temperatures of the bleed air ducts connected to the environmental control system below the auto ignition temperature of jet fuel/fuel vapors that may leak from adjacent wing and center fuel tanks. The bleed air is then further compressed in the compressor section of an air cycle machine. Additional cooling of the bleed air may be performed in a secondary heat exchanger, once again using ram air. The bleed air is then typically expanded to the desired pressure across the turbine section. The energy generated during the expansion process may be used to drive the compressor stage and also further drop the temperature of the bleed air. The cooled bleed air is mixed with cabin recirculation air to maintain the temperature of the air at a desired level.
It should be appreciated that while the environmental control system is necessary for operation of the aircraft, the weight of the system may have a less than desirable impact on the fuel performance or carrying capacity of the vehicle. Accordingly, while existing environmental control systems are suitable for their intended purposes the need for improvement remains, particularly in providing a lower weight heat exchanger.